As the complexity of integrated circuits has increased, the difficulty of determining whether a particular circuit is functional has increased considerably. In a well-known test method for integrated circuits, a charging circuit having a capacitor, after it has been charged, is discharged through pairs of input and output terminals of an integrated circuit to be tested, one pair at a time, to apply a test voltage so as to check for an abnormality or any change in the diode characteristic of each pair. In this type of check, both before and after each capacitor discharge the same magnitude of current is passed through the terminal pair and the potential across the terminals is read to see whether the readings differ before and after the test voltage is discharged by the capacitor.
This test method requires consecutive changeover of terminal pairs so that the checks on individual pairs can be proceeded with in a continuous manner. Manual changeover is not only inefficient but also demands considerable time.
One way of automatic changeover is the use of a changeover device with a relay circuit. However, this type of device is disadvantageous in that it requires a number of long wires equal to the number of input and output terminals in an integrated circuit to be tested. In addition, undesirable barrier capacitance occurring between a lead wire and ground increases in proportion to the length of the lead wire.
Consequently, the presence of this barrier capacitance can result in an error in measuring the potential discharged from the test capacitor.